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Progress of Organic Chemistry.

273

therefore, must be dated the first outline of a true analytical investigation of an organic compound.

The subsequent pursuit of this method of inquiry brought into more general use the habit of representing by formula what is called the rational constitution of a body. The results of analysis show the numerical proportions in which the several elementary bodies or their equivalents exist in the compounds examined, and enable chemists to represent their composition by formulæ, which are absolutely true as expressions of these results. In the simple case of oxalic acid, for example, analysis shows with certainty that its two constituents, carbon and oxygen, are present in it, in the proportion of two equivalents of the former (C) to three of the latter (03), and that it may, therefore, be truly represented by C2 O. But whether the three molecules or atoms of oxygen are united directly with the two of carbon, as may be represented by (2 C+3 0); or whether they are so arranged that two of carbon being united to two of oxygen (CO), this compound is united again with the third atom of oxygen as in (C, O+ 0); or whether two of a compound C O are united with this third of oxygen, as in (2C O+ 0); or whether finally, the well known gas, carbonic acid CO2, unites directly with the equally well known carbonic oxide CO, so as to form oxalic acid, then truly represented by (CO2+CO); — these molecular or theoretical questions are not at all touched upon by the empirical formula C, O, though that formula is absolutely true as a representation of the relative proportions, determined by accurate analyses, in which its constituents exist in oxalic acid.

The principle involved in the above illustration has, ever since 1814, occupied more or less of the attention of organic chemists. It has given occasion, at different periods, to violent controversies, often foolishly warm, and in the conduct of which a philosophical zeal for the truth has occasionally been overborne by individual feelings, and even by the spirit of national rivalry. But, although very different theoretical views have been successively taken, as knowledge advanced, by different chemists, in regard to the rational composition of sundry organic compounds, yet these very differences have promoted, in almost every instance, the advancement of the science. They have each suggested additional inquiries, and indicated the necessity of new and special analytical investigations; so that rational formulæ, embodying, as they often do, most valuable hypotheses or conjectures, have in reality become an element of further progress. And now it is regarded as a requisite, very desirable if not indispensable, in the formula for organic substances,

VOL. XCIV. NO. CXCI.

T

that they should express, not only the relative proportions of the elements of which the substances consist, but a probable grouping of the molecules also, by which their relations to other substances of analogous composition, and their principal chemical reactions may be suggested or explained. In more Southern Europe, Dumas, Boullay, Laurent, and Gerhardt have been most conspicuous in this division of chemical labour.

In 1814, Berzelius, in his published analyses, showed that the doctrine of chemical equivalents was applicable to organic as well as to inorganic compounds; and thus by the aid of symbols, in which each elementary substance was represented by the initial letter of its Latin name, he was enabled to construct formulæ, by which, as we have said, their composition, as determined by analyses, could be truly represented. But his view then was, and many followed him in adopting it, that in organic substances consisting of three elements - carbon, hydrogen, and oxygen- the constituents were united with each other directly into ternary combinations, such as may be under

C

stood by placing the molecules in this manner instead of

HO'

being first united by twos, as would be represented by such formulæ as CH+ O or C+HO. In this ternary mode of union he recognised also a clear and satisfactory distinction be tween organic compounds, and those of the inorganic kingdom in which only binary combinations had hitherto been recognised. Already, however, in 1819, when he published the great contribution to scientific mineralogy, of which we have already spoken, Berzelius intimated his belief that the electro-chemical theory was also capable of best explaining all the phenomena exhibited by organic bodies. This involved the opinion that organic compounds were all binary, and he now began to represent the organic acids as oxides of what are now well known in chemistry by the name of compound radicals.

These so-called radicals of Berzelius were for the most part hypothetical, only supposed or assumed to exist. It was to the brilliant researches of Gay Lussac, that we owed our first acquaintance with a compound body which exhibited all the chemical relations hitherto supposed to be characteristic of the elementary substances. His discovery of cyanogen, --- a compound of nitrogen and carbon, which behaved in every respect towards the elementary bodies as chlorine and iodine do, once astonished and enlightened the chemists of the time (1815), and was doubtless the germ of the new views soon after adopted by Berzelius (1819) and others, in reference to organic com

- at

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Compound Radicals.

275

binations. This was probably hastened also by the idea thrown out by Ampere, in 1816, that, as the compound cyanogen was analogous to the electro-negative elements, chlorine, iodine, &c., so the hypothetical compound ammonium, consisting of nitrogen and hydrogen (NH), resembled in all its chemical relations the large family of metals, or electro-positive elementary bodies. But cyanogen and the supposed ammonium contained two elementary bodies only; and although much progress was made in rational organic chemistry by the aid of these additions to our knowledge, yet much darkness and doubt existed still. In decomposing organic substances it had often been remarked that certain elements or certain proportions of their constituent elements, were separated from a compound more easily than others, and thus appeared to be held by a less powerful affinity, or to form less necessary portions of the molecular arrangement as a whole. Did the more firmly united molecules often containing three elements constitute a central radical, round which the others were grouped more loosely, from which the latter might be removed without breaking up the central arrangement, or with which, instead of the latter, other elements might be combined, without altogether taking away the characteristic properties of the compound into which they were introduced? Experience could not answer this question.

Years of active thought and research scarcely yet appeared to justify the supposition that radicals containing three elements really did exist. It was pushing theory much too far a-head of experiment, leaping too far into the unknown, to admit that radicals might exist of which oxygen, united to hydrogen and carbon, formed a part, and which should yet appear in their relations to chlorine, and the other elementary bodies, as if they were themselves simple and uncompounded. But the dawn of a new day had come, and a gleam of fresh light was thrown upon rational organic chemistry, when in 1832, a memoir on the composition and properties of benzoyl appeared, the joint production of Liebig and Wöhler. We can well recollect the surprise and pleasure expressed to ourselves by Berzelius on the perusal of the first account of their experiments; and every one at all acquainted with the later history of this branch of the science, must be aware, how much the results of these experiments have contributed to promote its rapid advancement. Since that period, indeed, Liebig has been gradually acquiring in Northern Europe, in reference to organic chemistry, a position approaching to that so long occupied by Berzelius, in reference to the science as a whole.

But the growing vastness of chemical knowledge forbids the idea of any second Berzelius ever appearing*, distinguished at once by special contributions to every branch, and by an intimate acquaintance, practical and theoretical, with the entire range of chemistry, mineral and organic. Future great chemists must be content to bear rule each in his own particular walk only.

It would weary our readers were we to indulge in further detail regarding the progress of organic chemistry in its pure state. That the so-called rational views on the composition of organic bodies have undergone serious alterations at brief intervals of time, and as knowledge widened, is a proof that our progress has been rapid. And again, the extent to which such changes have really taken place, is popularly shown by the successive new names which have in consequence been imposed on the same substance, and the burdensome synonymy which has thus been introduced into the science. We open at random a volume of the German Dictionary of Chemistry, to which we have already referred, and the following synonymy appears at the head of the first paragraph which catches our eye. Hydrochlorate of Chloride of Vinyl, Chloride of Elayl (Berzelius), -Hydrochlorate of Chloride of Acetyl (Liebig), Chloride of Etherin (Mitscherlich), Hydrochlorate of 'Chloride of Aldehydene (Regnault), Chloride of Hydrocarbon,Chloric Ether, Oil of Olefiant Gas,-Oil of the Dutch chemists, Dutch liquid.' Ten ponderous names for a useless oily liquid, discovered by some Dutch chemists in 1795, and which is produced when olefiant gas and chlorine gas are mixed together! Probably as many more may be

6

1

'The

* This difficulty of now mastering the science as he had been able to do, is put forward by Berzelius, in his Årsberättelse as far back as 1838 of course with a very different view from ours. 'period of my life,' he says, 'has been peculiarly favourable for the 'study of that science to which I have felt a natural inclination, and a similar one can never return. At the beginning of my scientific 'studies, new-born chemistry had scarcely left its cradle. The measure of existing knowledge did not exceed the capacity of youth to bear in mind. The whole was soon made familiar, though year by year it has been developed, and the measure of knowledge gradually increased. After forty years of progress, a mass of materials lies before the beginner of which it is impossible for him to make more than a part his own, within the period assigned to ordinary 'studies, and perhaps more than any one can ever altogether master, 'although it has not been difficult to become gradually possessed of 'all during a continued study of forty years.' Thirteen years of most rapid advance have elapsed since this was written,- how much more arduous, then, must the task be now!

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Changing Theories and Nomenclature.

277

given to it, before either its name is finally fixed, or its nature and rational formula truly determined. As marks of progress, real or imaginary, such a series of landmarks may be very interesting; but what human memory can hope to retain them all? With the view of simplifying, harmonising, and rendering uniform, the entire nomenclature of this organic department, Leopold Gmelin, in the fourth and fifth volumes of his most learned and most valuable Handbuch der Chemie,' has boldly coined an entirely new system of names which are intended to supersede all that had gone before. Regnault also, in the fourth volume of his excellent Cours Elémentaire 'de Chimie,' has introduced some beautiful theoretical simplifications into the nomenclature of certain classes of bodies which had been suggested by Dumas and others. Both attempts are entitled to great credit, more especially the laboriously developed and long digested scheme of Gmelin. His new names have the advantage of being intelligible through the synonymes that accompany them, which is not the case with those of Regnault. But the period has not yet arrived for fixing this nomenclature; and in both cases, we fear that the premature attempt will have only ended generally in new additions to the uncouth crowd of names by which the members of this class of bodies were previously known.

Among the most recent advances which have been made since the general reception of the doctrine of organic radicals, we may mention, on the one hand, the theoretical exposition of the doctrine of types and of organic replacement so ably set forth by Dumas; and on the other, the practical isolation of many radicals long supposed to exist but not hitherto obtained in a separate state-the preparation, by artificial processes, of numerous organic compounds possessed of alcaline properties, (organic alcalies)- and the similar artificial preparation of compounds which are naturally produced in the animal and vege table kingdoms. The two latter points are deserving of a brief illustration.

It was long believed that the compound bodies formed and found in the living organism, whether animal or vegetablewhich compose their tissues, or are contained in the fluids that fill their vessels-were specially produced by the agency of the principle of life; that in this agency consisted the main distinction between mineral and organic compounds; and that the production of the latter was beyond the reach of human art, operating upon mere dead matter. This belief has been gradually undermined by the progress of discovery. As early as 1811 it was known that starch and woody fibre could